1. Field of the Invention
The present invention relates to marine propellers, and more particularly to a marine propeller equipped with adjustable exhaust structures for allowing adjustment of exhaust volume.
2. Description of the Related Art
U.S. Pat. No. 5,916,003 discloses a propeller device, which comprises a propeller body with a propeller hub having 4 propeller blades extending therefrom and an aperture on each propeller blade, and a plug having a diametric profile shaped to be received and retained within each aperture. The vent plugs are provided with openings therethrough so that fluids can flow from a passage within a hub of the propeller device to a region proximate the outer cylindrical surface of the hub. The plugs can be changed to modify the size of the ventilation aperture without having to change the propeller device itself.
The propeller device is driven by an engine to move the propeller blades through water, achieving propeller thrust and forcing the boat to move forwards. At the same time, waste engine gas enters the passage of the propeller hub. At this time, a part of waste engine gas is exhausted through the ventilation aperture. Thus, the ventilation apertures of the plugs assist lowering the internal air pressure of the passage of the propeller hub, reducing water pressure from the propeller blades and enhancing propelling speed of the propeller blades.
However, under different application conditions, such as different water level, load, temperature, and etc., the user must selectively use different sizes of plugs having different dimensions of ventilation apertures, or plugs without any ventilation aperture to adjust the exhaust volume of the propeller device to an optimal condition for better propeller performance.
In other words, the user must provide different sizes of plugs having different dimensions of ventilation apertures for use in different conditions. Preparing a large number of plugs relatively increases the cost. Further, the plugs can get lost easily when not in use. Therefore, the aforesaid prior art design of propeller device is not convenient to use.